1. Field of the Invention
The invention relates to the chemical treatment of synthetic organic fibers and fabrics and more particularly relates to a method of coating organic fibers with polytetrafluoroethylene.
2. Brief Description of the Prior Art
Prior hereto it was known that synthetic and/or inorganic fabrics such as glass fabrics could be coated with polytetrafluoroethylene to improve their soil release properties and to enhance their durability; see for example U.S. Pat. No. 3,968,297. In the latter patent, the method of coating comprises first applying a base coat of a tetravalent titanium oxide polymer, a zirconium oxide polymer or a tin oxide polymer. The base coat is then top coated with an unsintered aqueous dispersion of polytetrafluoroethylene particles.
It has also been proposed heretofore to coat elastomeric materials such as butadiene-acrylonitrile copolymers with unsintered polytetrafluoroethylene particles by first softening the polymer surface with a solvent and adhering the polytetrafluoroethylene particles to the softened surface; see for example U.S. Pat. No. 3,200,006. In U.S. Pat. No. 3,511,682 a method is described wherein the elastomer is coated with a thin film of polytetrafluoroethylene and then the film is sintered with an open flame on the elastomer surface.
It will be appreciated by those skilled in the art that the prior art methods of coating both inorganic and organic materials requires multiple treatment steps, specific base coats, solvents and/or sintering with relatively high temperatures. Such procedures may weaken certain synthetic organic fibers and fabrics such as polyaramids. By the method of my invention, synthetic organic fibers and fabrics such as polyaramids may be coated with polytetrafluoroethylene, improving their soil release characteristics, acid resistance, hydrophobicity and oleophobicity in a single step, without the need for solvents, flames, exotic base coats and the like. The method of my invention does not adversely affect the treated fibers, i.e.; does not weaken, stiffen or otherwise alter the desired basic properties for which the fibers and fabrics were selected. The method of my invention is particularly advantageous for the treatment of filter fabrics prepared from synthetic, organic fiber materials. The treated filter fabrics are particularly useful for air filtration under circumstances wherein the filter fabric will be exposed to acid vapors.